For the purpose of improving the feel and travel distance of golf balls on full shots with different clubs, development of golf balls using various elastomers in the intermediate layer or the cover is currently in progress. Such golf balls are disclosed, for example, in U.S. Pat. No. 5,556,098, JP-A 10-108923 and U.S. Pat. No. 6,315,680.
More particularly, Higuchi et al., U.S. Pat. No. 5,556,098, assigned to the same assignee as the present invention, describes a three-piece solid golf ball using a polyester thermoplastic elastomer in the intermediate layer and an ionomer resin in the cover. Since the intermediate layer and the cover are made of different materials, a problem arises in the bond therebetween. The ball is somewhat less durable against repeated shots.
JP-A 10-108923 describes a multi-piece solid golf ball using a mixture of a polyurethane thermoplastic resin and an ionomer resin in the intermediate layer. Since the cover is made of an ionomer resin, the ball yet suffers from durability and needs some improvement in rebound.
Dalton et al., U.S. Pat. No. 6,315,680 describes a golf ball comprising a hard mantle layer having a Shore D hardness greater than 60 and comprised of a thermoplastic polyurethane or a thermoplastic polyester. Due to the hard mantle layer, the ball gives an unpleasant feel when hit with short irons, typically iron No. 9, and needs some improvement in rebound.
These golf balls use relatively soft cover materials as typified by ionomer resins as mentioned above. Upon repeated shots, the balls are likely to be scraped by the abutment of the edge and head of iron clubs against the ball surface. The balls are less resistant to scuffing as well. Upon repeated shots, cracks can occur. These indicate insufficient durability against repeated impact.
On the other hand, one-piece balls having improved durability and two-piece balls having relatively good flight performance are used as practice golf balls. However, the one-piece balls largely differ from balls for normal play in that they are extremely low in rebound and upon full shots with a driver or iron, follow a high-rise trajectory due to excessive spin reception.
The two-piece balls for practice have a cover of a hard ionomer resin. They receive a spin rate which is too low as compared with the quality balls professional and skilled golfers use on the course. The balls are less resistant to scuffing as well. These balls are thus inadequate for professional and skilled golfers to use in practice.
Among the quality balls professional and skilled golfers currently play on the course, multi-piece solid golf balls, typically three-piece solid golf balls using polyurethane elastomer as the cover enjoy widespread use. These balls are excellent in properties including flight, feel and spin, and fairly improved in durability. However, the durability is insufficient as the balls to be repeatedly hit numerous times for practice purposes.
JP-A 2001-54588 discloses a three-piece golf ball using a thermoplastic polyurethane elastomer as the cover. The polyurethane elastomer forms a poor bond with the ionomer resin of which the intermediate layer is formed. As a result, a primer must be applied to the intermediate layer after the intermediate layer is formed around the core and before the cover is formed thereon. There is left a room for improvement in productivity.
JP-A 9-215778 describes a two-piece golf ball using a thermoplastic polyurethane elastomer as the cover. This two-piece golf ball does not give rise to the poor bond problem as mentioned just above, but receives too much spin on shots with a driver or iron and hence, travels a rather skying trajectory, as compared with the three-piece ball having a high hardness intermediate layer between the cover and the core.